Thanks for that Geoff at 58 I sometimes don't feel that young !!
As I think people have said, ultimately it's down to a number of factors - health, strength and just whether you "feel" like riding.
Anyway as I said the plan is to keep going for as long as I can, even if that does mean st some point downsizing (moving to a lighter / less powerful) bike.
Who knows at some time in the future there might be an 80 year old riding a smokey H2 around Somerset...............